(a) Technical Field
The present invention relates to an end plate for a fuel cell including an anti-bending plate. More particularly, it relates to an end plate for a fuel cell including an anti-bending plate, in which an anti-bending plate is assembled with an insert having a sandwich-like structure and the insert is injection molded, thereby easily preventing the insert from being bent due to an injection molding pressure.
(b) Background Art
Referring to FIG. 10, in a unit cell of a fuel cell stack mounted on a fuel cell vehicle, a Membrane-Electrode Assembly (MEA) is located at the innermost side of the unit cell of the fuel cell stack. The MEA includes a solid polymer electrolyte membrane 10 through which protons pass and catalytic electrode layers, i.e., a cathode 12 and an anode 14, coated on opposite surfaces of the solid polymer electrolyte membrane 10 such that hydrogen can react with oxygen. Gas Diffusion Layers (GDL) 16 and gaskets 18 are sequentially staked outside the cathode 12 and the anode 14, and separation plates 20 including flow fields for supplying fuel and discharging water generated by the reaction are located outside the GDLs 16.
After several hundred unit cells are stacked, end plates 30 for supplying and fixing each of the unit cells are assembled at the outermost sides of the fuel cell stack. In this case, a current collector plate for collecting electricity generated in the fuel cell stack and sending the collected electricity to outside of the fuel cell stack is mounted inside the end plates 30.
An oxidation reaction of hydrogen occurs in the anode 14 of the fuel cell stack and protons and electrons are generated by the reaction. At this time, the generated protons and electrons flow to the cathode 12 respectively through the solid polymer electrolyte membrane 10 and the separation plate 20, so that water is generated in the cathode 12 through an electrochemical reaction of the protons and electrons from the anode 14 with oxygen in the air and electrical energy, finally generated through flow of the electrons, is supplied to a load requiring electrical energy through the current collector plate of the end plates 30.
The end plates 30 of the fuel cell stack serve to fasten a plurality of stacked separation plates, MEAs, and GDLs and simultaneously serve to provide a uniform surface pressure to each unit cell from opposite sides of the fuel cell stack respectively.
As can be seen in FIG. 9, the end plate 30 is formed with a metal insert 31, a plastic injection molded body 32, and a current collector plate 33, which are integrally formed, for weight reduction and electrical insulation. That is, the metal insert 31 is disposed inside an injection mold and then a plastic injection molding material is filled in the injection mold, thereby embodying the end plate 30 including the metal insert 31 surrounded by the plastic injection molded body 32.
In the meantime, the current collector plate 33 is disposed inside the injection mold together with the metal insert 31 and is injection molded together with the plastic injection molded body 32 or separately assembled inside the plastic injection molded body 32 later.
The metal insert of the end plate is required to have a high strength to resist an inner surface pressure. Accordingly, the metal insert is generally manufactured through machining of a metal material and also is manufactured in a complex shape to collect generated electricity from reactions within the fuel cell stack and fasten the fuel cell stack together securely.
However, a conventional metal insert of the end plate is manufactured in an integral shape, so that it has the following disadvantages:
First, in machining a material-reduction structure for weight reduction of the metal insert, it is difficult to perform injection molding for the metal insert. That is, a recess or an uneven portion should not be generated on a resin surface after the injection molding of the end plates, for assuring continuous contact with the gaskets to prevent a fuel leak. However, in applying the material-reduction structure to the metal insert, if a thickness of the resin material of the plastic injection molded body is not uniform, a recess or an uneven portion is disadvantageously generated on the surface of the resin due to the resin's contraction. In particular, if a pocket processing is performed to apply the material-reduction structure to the integral metal insert for reducing the weight, it is difficult to uniformly maintain the thickness of the injection molding material.
Second, the integral metal insert is manufactured by cutting a metal plate or a non-metal plate through machining, so it takes a long time to manufacture a single integral metal insert, thereby making it difficult to mass produce and reduce costs accordingly.
Third, the integral metal insert should be made of a single material. Therefore, applying different materials for weight reduction and strength improvement is also difficult.
In this respect, contrary to a conventional integral metal insert, a sandwich insert in which two or more plates each having a specific shape are stacked has been manufactured to maintain strength and simultaneously promote weight reduction. However, since the sandwich insert employs the centrally disposed plate having material-reduction spaces among several plates of the sandwich insert, the central portion of the sandwich insert is often bent due to resin pressure in the injection molding process for surrounding the sandwich insert with the plastic injection molded body.